When the reactor was restarted from an off-line state, the reactor output had to be confined to within 300 and 312 millicochranes to prevent fusion of the dilithium matrix, unless the spatial compression index was greater than 5.62 percent, or the ship was within two parsecs of a class C gravimetric field distortion. (ENT: "Doctor's Orders")

If the antimatter flow regulators are locked open, plasma pressure within the chamber will rise, threatening to destroy the ship. In order to reduce the pressure, the ship must maintain high warp until the damage is repaired. Such an event occurred in November of 2154, due to Klingonsabotage of the Enterprise NX-01. Moments before the engine was shut down and cold started, intermix pressure had risen to 1527 and the field variance had risen to 87 millicochranes. (ENT: "Affliction")

In the original configuration, warp factor 5 was the maximum speed that could be maintained by a ship using the warp five engine for 53 minutes only. This speed was first tested in 2152. (ENT: "Fallen Hero") By 2153, warp 5 had become a sustainable cruising velocity that could be maintained for long periods of time. The speed of warp 5 corresponded roughly to a velocity of 200 times the speed of light. (ENT: "The Expanse", "The Xindi")

In the episode "The Expanse", a location was given to Archer on where to go look for the Xindi inside the Delphic Expanse. The location was stated to be a three month trip away from Earth at warp 5. In the next episode, "The Xindi", when Enterprise had arrived to look for the Xindi in that region, it was said they were 50 light years away from Earth. This indicates warp 5 equals to a speed of approximately 200 times the speed of light.

The warp five engine used by the Terran Empire, in the mirror universe, was known to leak delta rays. The radiation caused severe disfigurement to the engineers who worked on them. It was said that for every year an engineer spent next to one, he lost a decade of his life expectancy. (ENT: "In a Mirror, Darkly")

The plasma injector assembly of the reactor was upgraded in 2154, to allow a ship to maintain the speed of warp 5.06. (ENT: "Babel One") After the upgrade, the speed of warp 5.2 could also be reached for short periods of time. (ENT: "Affliction")

The injector assembly could also be easily modified, based on Haradin schematics, to allow a ship to reach the speed of warp 6.9 for short intervals using the warp five engine. The structural integrity also needed to be reinforced on the NX-class ships for this to be possible. It was however determined that using the Haradin modification, the injectors might overload at speeds over warp factor 5.6. Due to the risk these speeds were not used by the Enterprise. (ENT: "E²")